1. Field of the Invention
The present invention relates to an apparatus for controlling a starting clutch made up of a hydraulic clutch provided in a transmission of a vehicle having a function of stopping engine idling in which an engine is automatically stopped under given conditions when the vehicle is at a standstill.
2. Description of Related Art
Conventionally, there is known an apparatus for controlling a hydraulic oil pressure in a starting clutch by a linear solenoid valve which is provided in a hydraulic circuit. The hydraulic circuit has, as a hydraulic oil pressure source, a hydraulic oil pump to be driven by an engine of a vehicle. In an ordinary vehicle in which engine idling is continued when the vehicle is at a standstill, the following steps are taken. Namely, at the time of vehicle start-up, a command signal is given to the linear solenoid valve such that the hydraulic oil pressure in the starting clutch (starting clutch pressure) becomes a creeping pressure at which the vehicle gives rise to creeping. Once the vehicle has started up, the starting clutch pressure is increased (or boosted) to a hydraulic oil pressure which is the pressure at the time of an ordinary running of the vehicle.
On the other hand, in a vehicle having a function of stopping engine idling, a hydraulic oil pressure in a hydraulic circuit becomes zero as a result of stopping the engine when the vehicle is at a standstill. At the time of vehicle start-up from this state, if a command signal to raise the starting clutch pressure is given to a linear solenoid valve, the linear solenoid valve becomes fully opened. Therefore, when the hydraulic oil pressure in the hydraulic circuit has risen as a result of starting the drive of the hydraulic oil pump accompanied by the starting of the engine, the starting clutch pressure will overshoot to a value exceeding the command value. Therefore, if the command value of the starting clutch pressure has already become the creeping pressure, the starting clutch pressure exceeds the creeping pressure. As a result, the starting clutch is rapidly engaged to thereby give rise to shocks.
In view of the above points, the present invention has an object of providing an apparatus for controlling a starting clutch in a vehicle having a function of stopping engine idling, in which the vehicle start-up from the state of engine stopping can be made smoothly and at a good response.
In order to attain the above and other objects, the present invention is an apparatus for controlling a starting clutch made up of a hydraulic clutch provided in a transmission of a vehicle having a function of stopping engine idling so that an engine is automatically stopped under given conditions when the vehicle is at a standstill, wherein a hydraulic oil pressure in the starting clutch is controlled by a linear solenoid valve provided in a hydraulic circuit having, as a hydraulic oil pressure source, a hydraulic oil pump driven by the engine, the apparatus comprising: first hydraulic oil pressure command means which, at a time of vehicle start-up from a state of engine stopping, sets that hydraulic oil pressure command value in the starting clutch which is controlled by the linear solenoid valve to a predetermined initial pressure until the hydraulic oil pressure in the hydraulic circuit rises, the initial pressure being lower than a creeping pressure at which creeping of the vehicle occurs; second hydraulic oil pressure command means which, during a predetermined period of time from a time at which the hydraulic oil pressure in the hydraulic circuit has risen to a time at which the hydraulic oil pressure increases to the creeping pressure, changes the hydraulic oil pressure command value to an ineffective stroke eliminating pressure which is higher than the creeping pressure; and third hydraulic oil pressure command means which changes the hydraulic oil pressure command value to the creeping pressure after a lapse of the predetermined period of time.
According to the present invention, the hydraulic oil pressure command value at the beginning of the vehicle start-up becomes the initial pressure which is lower than the creeping pressure. Therefore, even if there is no residual pressure in the hydraulic circuit and the linear solenoid valve is thus fully opened, with the result that the hydraulic oil pressure in the starting clutch (starting clutch pressure) overshoots the hydraulic oil pressure command value when the hydraulic oil pressure in the hydraulic circuit has risen, the starting clutch pressure will become a pressure about the creeping pressure. Shocks will therefore not occur.
It is also considered to switch the hydraulic oil pressure command value to the creeping pressure when the hydraulic oil pressure in the hydraulic circuit has risen. This method, however, has the following disadvantage. Namely, it takes time to eliminate or minimize the ineffective stroke of the starting clutch and, therefore, the pressure increase (boosting) in the starting clutch pressure is delayed, resulting in a larger time lag in the vehicle start-up.
In the present invention, on the other hand, the hydraulic oil pressure command value is switched to an ineffective stroke eliminating pressure which is higher than the creeping pressure when the hydraulic oil pressure in the hydraulic circuit has risen. The ineffective stroke of the starting clutch can therefore be eliminated or minimized at a short time. By subsequently switching the hydraulic oil pressure command value to the creeping pressure, the starting clutch pressure can be quickly increased to the creeping pressure without giving rise to overshooting. In this manner, the vehicle start-up from the state of engine stopping can be performed smoothly and at a good response.
It is also possible to provide a hydraulic oil pressure sensor to detect the hydraulic oil pressure in the hydraulic circuit. When the pressure rise in the hydraulic circuit has been detected by the hydraulic oil pressure sensor, the hydraulic oil pressure command value is switched from the initial pressure to the ineffective stroke eliminating pressure. This method, however, becomes higher in cost.
If the hydraulic oil pressure in the hydraulic circuit rises in a state in which the linear solenoid valve is fully opened, the linear solenoid valve is returned toward the closed position. A counter-electromotive force will then be generated in a solenoid of the linear solenoid valve. Therefore, by providing means for discriminating a rise in the hydraulic oil pressure in the hydraulic circuit (first discriminating means for discriminating a rise in the hydraulic oil pressure) based on the counter-electromagnetic force to be generated in the solenoid of the linear solenoid valve, the cost increase can be avoided. In this arrangement, should the hydraulic oil pressure vary even slightly, the counter-electromotive force will be generated, and there is a possibility of making a wrong discrimination. It is therefore preferable to provide prohibiting means for prohibiting the discrimination by the first discriminating means until a rotational speed of the engine increases to a certain value (a first predetermined speed).
In case there is a residual pressure in the hydraulic circuit because the vehicle is right after the engine stopping, the linear solenoid valve will not be fully opened. Therefore, it becomes difficult to discriminate the rise in the hydraulic oil pressure by means of the counter-electromotive force which is generated in the solenoid of the linear solenoid valve. It is to be noted here that, when the rotational speed of the engine exceeds a certain value (a second predetermined speed), the hydraulic oil pressure in the hydraulic circuit surely rises. Therefore, it is preferable to provide means for discriminating (second discriminating means for discriminating a rise in the hydraulic oil pressure) that the hydraulic oil pressure has risen when the rotational speed of the engine has increased to a second predetermined speed so as to cope with the vehicle start-up in a state in which there is a residual pressure in the hydraulic circuit.
In order to detect that rotational speed of the engine which serves as a discriminating parameter in the above-described prohibiting means and the second discriminating means for discriminating a rise in the hydraulic oil pressure, it is considered to provide a rotational speed sensor which is made up of a pulser gear mounted on a crank shaft and a pickup. This solution, however, becomes higher in cost. To reduce the cost, it is considered to input the engine ignition pulses into an onboard (vehicle-mounted) computer so that the rotational speed of the engine is calculated from the difference in time of inputting the engine ignition pulses of the engine. However, the engine ignition pulses are inputted only in number corresponding to the number of cylinders of the engine within two rotations of the crank shaft. At the time of rapid increase in the rotational speed of the engine such as at the time of vehicle start-up from the state of engine stopping, the rotational speed of the engine to be calculated from the difference in time of inputting the engine ignition pulses becomes considerably smaller than the actual rotational speed of the engine. In this case, it is preferable to make the following arrangement. Namely, a rotational speed to be calculated by a difference between a time of inputting a first engine ignition pulse and a time of inputting a second engine ignition pulse, both pulses being inputted after the engine stopping, is defined as a provisional speed, and a point of time at which the rotational speed of the engine increases to the first predetermined speed is obtained from the provisional speed. Further, at the time of vehicle start-up from a state in which the engine is not completely stopped, out of rotational speeds to be calculated by a difference between times of inputting two consecutive engine ignition pulses, a first rotational speed at which the rotational speed has changed for an increase is defined to be a provisional speed, and a point of time at which the rotational speed of the engine increases to the first predetermined speed is obtained from the provisional speed. By this arrangement, the accuracy of discrimination based on the rotational speed of the engine in the above-described prohibiting means and the above-described second discriminating means for the rise in the hydraulic oil pressure can be improved.
Further, in a vehicle in which the transmission has a belt-type continuously variable transmission mechanism which is provided on an input side of the starting clutch and which inputs the power from the engine through a power transmission mechanism such as a forward/reverse switching mechanism having built-in hydraulically operated frictional elements, when there is a residual pressure in the hydraulic circuit, the power transmission mechanism is maintained in a state which is capable of transmitting the power. Consequently, with the start of the engine, the drive pulley of the continuously variable transmission mechanism is also rotated. Therefore, there may be provided means for discriminating that the hydraulic oil pressure has risen (third discriminating means for discriminating a rise in the hydraulic oil pressure) when the rotational speed of the drive pulley has increased to a predetermined speed.
In the preferred embodiments which are described in detail hereinbelow, what corresponds to the above-described first hydraulic oil pressure command means is step S6 in FIG. 3. What corresponds to the above-described second hydraulic oil pressure command means is step S11 in FIG. 3. What corresponds to the above-described third hydraulic oil pressure command means is step S16 in FIG. 3. What corresponds to the above-described first discriminating means for discriminating a rise in the hydraulic oil pressure is step S4-26 in FIG. 4. What corresponds to the above-described prohibiting means is step S4-24 in FIG. 4. What corresponds to the above-described second hydraulic oil pressure rise discriminating means is step S4-32 in FIG. 4. What corresponds to the above-described third hydraulic oil pressure rise discriminating means is step S4-31 in FIG. 4.